Synthesis of Ordered Mesoporous Silica with Nonionic Surfactant/Anionic Polyelectrolyte as Template under Near-Neutral pH Conditions.

Ordered mesoporous silica is widely used in catalysis, adsorption, and biomedicine, among which SBA-15 (Santa Barbara Amorphous-15) is one of the most widely studied. However, the synthesis of SBA-15 often requires strong acid (hydrochloric acid or sulfuric acid), which will not only corrode industrial equipment but also pollute the environment with the wastewater containing strong acid and halogen (sulfur). Here, we demonstrate a green synthetic strategy for SBA-15 under weakly acidic conditions through an anionic assembly route. With the assistance of poly(acrylic acid) (PAA) and 3-aminopropyltrimethoxysilane (APMS), the pH value of the synthesis system can be increased to 4-5, which is a mild near-neutral condition. In addition, halogen-free synthesis using organic acids is also achieved. The powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 sorption characterizations show that the obtained SBA-15 has good texture properties, with a specific surface area of 430-500 m2/g and ordered 6-8 nm mesopores, which is similar to SBA-15 synthesized in traditional strong acid. This strategy provides a facile and environmentally friendly route for the large-scale production of ordered mesoporous materials.

Amorphous CeOx Islands on Dealuminated Zeolite Beta to Stabilize Pt Nanoparticles as Efficient and Antisintering Catalysts for Propane Dehydrogenation.

Pt-based catalysts have been widely used in propane dehydrogenation due to their superior activation of C-H bonds and weak scission of C-C bonds. However, in the process of repeated calcination to remove deposited coke, the active Pt species tend to sinter, resulting in a significant decline in catalytic activity. In this study, amorphous CeOx islands loaded on dealuminated Beta zeolite were prepared via simple wetness impregnation. Then, partially embedded Pt nanoparticles in CeOx islands were obtained after reduction owing to the affinity of CeOx for Pt. In the propane dehydrogenation reaction, Pt/Ce5-SiBeta with a Ce loading of 4.55 wt % and Pt loading of 0.72 wt % exhibited the highest activity and the lowest inactivation constant at 550 °C. More importantly, due to the anchoring effect of CeOx on Pt, the catalytic activity of Pt could be recovered after a simple calcination-reduction regeneration process, avoiding the chlorination treatment for the redispersion of Pt species used in industry. In addition, to improve the selectivity of the Pt/Ce5-SiBeta catalyst, a PtSn/Ce5-SiBeta catalyst with excellent activity, selectivity, and recycling stability has been prepared by introducing Sn into Pt/Ce5-SiBeta. The use of amorphous CeOx islands to improve the sintering resistance of Pt opens up new prospects for the design of stable industrial dehydrogenation catalysts.

Research Progress on Porous Carbon-Based Non-Precious Metal Electrocatalysts.

The development of efficient, stable, and economic electrocatalysts are key to the large-scale application of electrochemical energy conversion. Porous carbon-based non-precious metal electrocatalysts are considered to be the most promising materials to replace Pt-based catalysts, which are limited in large-scale applications due to high costs. Because of its high specific surface area and easily regulated structure, a porous carbon matrix is conducive to the dispersion of active sites and mass transfer, showing great potential in electrocatalysis. This review will focus on porous carbon-based non-precious metal electrocatalysts and summarize their new progress, focusing on the synthesis and design of porous carbon matrix, metal-free carbon-based catalysts, non-previous metal monatomic carbon-based catalyst, and non-precious metal nanoparticle carbon-based catalysts. In addition, current challenges and future trends will be discussed for better development of porous carbon-based non-precious metal electrocatalysts.

Synthesis of Hierarchically Porous Bioactive Glass and Its Mineralization Activity.

Mesoporous bioactive glass is a promising biomaterial for bone tissue engineering due to its good biocompatibility and bioactivity. In this work, we synthesized a hierarchically porous bioactive glass (HPBG) using polyelectrolyte-surfactant mesomorphous complex as template. Through the interaction with silicate oligomers, calcium and phosphorus sources were successfully introduced into the synthesis of hierarchically porous silica, and HPBG with ordered mesoporous and nanoporous structures was obtained. The morphology, pore structure and particle size of HPBG can be controlled by adding block copolymer as co-template or adjusting the synthesis parameters. The ability to induce hydroxyapatite deposition in simulated body fluids (SBF) demonstrated the good in vitro bioactivity of HPBG. Overall, this work provides a general method for the synthesis of hierarchically porous bioactive glasses.

Hierarchically Porous Three-Dimensional (3D) Carbon Nanorod Networks with a High Content of FeNx Sites for Efficient Oxygen Reduction Reaction.

Efficient, durable, and inexpensive electrocatalysts are recommendable for accelerating the kinetics of oxygen reduction reaction and achieving high performance. Herein, with predesigned hierarchically porous silica nanorods as a hard template, hierarchically macro-bimodal meso/microporous 3D carbon interwoven nanorod networks containing a high content of single-atom FeNx species (Fe/RNC) were prepared by melting of precursors and confined pyrolysis within the pores of the hard template. What distinguishes the use of silica nanorods as a hard template is that it not only provides a porous texture for confined pyrolysis of the precursors but also the interwoven texture of the nanorods gives rise to a macroporous mesh-like morphology. Benefiting from the ultrahigh iron content (5.69 wt %) of the FeNx sites, a 3D porous network configuration with high accessibility of active centers, as well as a high specific surface area of 793 m2g-1, the as-prepared Fe/RNC exhibited superior activity and durability for ORR and zinc-air batteries. For comparison, the catalyst Fe/NC-MCM, which was prepared with a similar procedure but with unimodal mesoporous silica MCM-41 nanoparticles as the hard template, possesses a less porous structure and active accessibility and thus exhibits inferior ORR activity. This work provides an effective design/nanoengineering for electrocatalysts in ORR and zinc-air batteries and will inspire more research on accessibility of active sites in non-noble carbon-based electrocatalysts.

Hierarchically Porous Mesostructured Polydopamine Nanospheres and Derived Carbon for Supercapacitors.

Polydopamine (PDA), with similar chemical and physical properties to eumelanin, is a typical artificial melanin material. With various functional groups, good biocompatibility, and photothermal conversion ability, PDA attracts great interest and is extensively studied. Endowing PDA with a porous structure would increase its specific surface area, therefore would significantly improve its performance in different application fields. However, creating abundant pores within the PDA matrix is a great challenge. Herein, a self-assembly/etching method is proposed to prepare hierarchically porous mesostructured PDA nanospheres. The oxidative polymerization of dopamine and hydrolysis of tetraethyl orthosilicate were coupled to co-assemble with a polyelectrolyte-surfactant complex template to form a mesostructured PDA/silicate nanocomposite. After removing templates and etching of silica, hierarchically porous PDA nanospheres were obtained with specific surface area and pore volume as high as 302 m2 g-1 and 0.67 cm3 g-1, respectively. Moreover, via subsequent carbonization and silica-etching, ordered mesoporous N-doped carbon microspheres (OMCMs) with ∼2 nm ordered mesopores and ∼20 nm secondary nanopores could be obtained. When used as electrodes of supercapacitors, the OMCMs exhibited a specific capacity of 341 F g-1 at 1 A g-1 with excellent rate capability, and the OMCM-based symmetric supercapacitor delivered a high energy density of 14.1 W h kg-1 at a power density of 250 W kg-1 and minor capacitance fading (only 2.6%) after 10,000 cycles at 2 A g-1.

New insights into the NH3-selective catalytic reduction of NO over Cu-ZSM-5 as revealed by operando spectroscopy.

To control diesel vehicle NO x emissions, Cu-exchanged zeolites have been applied in the selective catalytic reduction (SCR) of NO using NH3 as reductant. However, the harsh hydrothermal environment of tailpipe conditions causes irreversible catalyst deactivation. The aggregation of isolated Cu2+ brings about unselective ammonia oxidation along with the main NH3-SCR reaction. An unusual 'dip' shaped NO conversion curve was observed in the steamed zeolite Cu-ZSM-5, resulting from the undesired NH3 oxidation that produced NO. Here we gain further insights into the NH3-SCR reaction and its deactivation by employing operando UV-vis diffuse reflectance spectroscopy (DRS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) on fresh and steamed zeolite Cu-ZSM-5. We found that tetragonally distorted octahedral Cu2+ with associated NH3 preferentially forms during low temperature NH3-SCR (<250 °C) in fresh Cu-ZSM-5. The high coordination number of Cu2+ ensures the availability for high coverage of nitrate intermediates. Whilst in the steamed Cu-ZSM-5, [Cu x (OH)2x-1]+ oligomers/clusters in pseudo-tetrahedral symmetry with coordinated NH3 accumulated during the low-temperature NH3-SCR reaction. These clusters presented a strong adsorption of surface NH3 and nitrates/nitric acid at low temperatures and therefore limited the reaction between surface species in the steamed Cu-ZSM-5. Further release of NH3 with increased reaction temperature favors NH3 oxidation that causes the drop of NO conversion at ∼275 °C. Moreover, competitive adsorption of NH3 and nitrates/nitric acid occurs on shared Lewis-acidic adsorption sites. Prompt removal of surface nitrates/nitric acid by NO avoids the surface blockage and tunes the selectivity by alternating nitrate-nitrite equilibrium. The formation of adsorbed NO2 and HNO x points to the necessity of an acid adsorbent in practical applications. The structural similarity under the NH3-SCR reaction and unselective NH3 oxidation confirmed the entanglement of these two reactions above 250 °C.

Steam-assisted strategy to fabricate Anatase-free hierarchical titanium Silicalite-1 Single-Crystal for oxidative desulfurization.

As an important heterogeneous catalyst, Titanium Silicalite-1 (TS-1) zeolite has been widely applied in various catalytic processes. Here, hierarchical TS-1 single-crystals were successfully synthesized by a steam-assisted crystallization strategy using hierarchically porous titanium-containing silica (Ti-NKM-5) as a precursor. Due to the presence of large mesopores (10-40 nm)， the microporous structure-directing agents penetrated the interstitial structure of silica particles, inducing the dissolution and crystallization process. During crystallization, the generated nanocrystals grew together to form a hierarchical structure. Titanium was fully incorporated into the zeolite framework, and no extra-framework anatase was formed. Compared with the traditional microporous TS-1 zeolite, the synthesized hierarchical TS-1 single-crystal exhibited superior catalytic performance in oxidative desulfurization (ODS) of dibenzothiophene (DBT) and 4, 6-dimethyl dibenzothiophene (4, 6-DMDBT) owing to the hierarchically porous and anatase-free structure. The recycling test revealed the durability of the obtained hierarchical TS-1 catalyst under moderate reaction conditions.

In-situ growth of cobalt manganate spinel nanodots on carbon black toward high-performance zinc-air battery: Dual functions of 3-aminopropyltriethoxysilane.

Developing cost-effective and stable non-noble electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is now the critical issue for large-scale application of zinc-air batteries. Here, we presented a simple method to synthesize highly dispersed cobalt manganate spinel nanodots in-situ embedded in amine-functionalized carbon black. Silane coupling agent 3-aminopropyltriethoxysilane (APTES) played dual roles in the preparation: (1) to achieve amine-functionalization of carbon support; (2) as weak alkali to precipitate metal hydroxides which were then converted to spinel nanodots after mild calcination. The hydrophilicity of the carbon substrate was enhanced by amine modification from APTES to disperse metal oxide evenly, and the electrochemical activity was promoted through the strong interface interaction between embedded spinel nanodots and carbon substrate during the calcination process. As expected, the CoMn2O4/C-NH2-300 catalyst exhibited satisfactory bifunctional catalytic performance for both ORR and OER with an ΔE (E1/2-Ej10) = 0.75 V, which was lower than most state-of-the-art catalysts. In addition, CoMn2O4/C-NH2-300 as a cathode also exhibited remarkable zinc-air battery performance in alkaline solution. This strategy of APTES as a bifunctional coupling agent provided a novel way to design and explore highly active, durable, and cost-effective catalysts for renewable energy conversion and storage.

Fluorescent, electrically responsive and ultratough self-healing hydrogels via bioinspired all-in-one hierarchical micelles.

Intelligent hydrogels that simultaneously exhibit excellent toughness, self-healing ability and photoelectronic responsiveness are in high demand but are greatly challenging to prepare. Inspired by the hierarchical structure of fluorescent proteins in jellyfish and biomembranes in nature, herein, a facile and universal all-in-one strategy is demonstrated to construct fluorescent, electrically responsive and ultratough self-healing hydrogels via aqueous self-assembly of polyelectrolyte-surfactant micelles with hierarchical structures and functionality. The self-assembled 2-ureido-4-[1H]-pyrimidone (UPy) hydrophobic core containing reversible physical crosslinks embedded in micelles leads to a durable network structure with excellent toughness and self-healing ability. Moreover, dramatically enhanced fluorescence emission is obtained due to the formation of nanoclusters with electron-rich moieties that show restricted intramolecular motion induced by hydrogen bonding networks from UPy dimer aggregation. The micelle-incorporated sulfonic acid groups mimic the function of biological membrane proteins that deftly control the micelle size, leading to electro-responsiveness, enhanced toughness and fluorescence emission.

Zeolite-Tailored Active Site Proximity for the Efficient Production of Pentanoic Biofuels.

Biofuel production can alleviate reliance on fossil resources and thus carbon dioxide emission. Hydrodeoxygenation (HDO) refers collectively to a series of important biorefinery processes to produce biofuels. Here, well-dispersed and ultra-small Ru metal nanoclusters (ca. 1 nm), confined within the micropores of zeolite Y, provide the required active site intimacy, which significantly boosts the chemoselectivity towards the production of pentanoic biofuels in the direct, one-pot HDO of neat ethyl levulinate. Crucial for improving catalyst stability is the addition of La, which upholds the confined proximity by preventing zeolite lattice deconstruction during catalysis. We have established and extended an understanding of the "intimacy criterion" in catalytic biomass valorization. These findings bring new understanding of HDO reactions over confined proximity sites, leading to potential application for pentanoic biofuels in biomass conversion.

Porous Noble Metal Electrocatalysts: Synthesis, Performance, and Development.

Active sites (intrinsic activity, quantity, and distribution), electron transfer, and mass diffusion are three important factors affecting the performance of electrocatalysts. Composed of highly active components which are built into various network structures, porous noble metal is an inherently promising electrocatalysts. In recent years, great efforts have been made to explore new efficient synthesis methods and establish structural-performance relationships in the field of porous noble metal electrocatalysis. In this review, the very recent progress in strategies for preparing porous noble metal, including innovation and deeper understanding of traditional methods is summarized. A discussion of relationship between porous noble metal structure and electrocatalytic performance, such as accessibility of active sites, connectivity of skeleton structures, channels dimensions, and hierarchical structures, is provided.

Enhanced Terahertz Amplification Based on Photo-Excited Graphene-Dielectric Hybrid Metasurface.

Graphene under optical pump has been shown to be an attractive gain medium with negative dynamic conductivity at terahertz frequencies. However, the amplification over a monolayer graphene is very weak due to its one-atom thickness. In this paper, the proposed graphene-dielectric reflective metasurface effectively improved terahertz field localization and enhanced coherent amplification. The amplification coefficient of 35 was obtained at 3.38 THz at room temperature with an infrared pump intensity of 8 W/mm2. As pump intensity increased from 0 to 15 W/mm2, we observed a loss-gain-loss transition process, which was discussed in detail through coupled-mode theory. In addition, amplification at different frequencies was achieved by merely re-optimizing the geometric parameters of the dielectric resonators. This study offers an effective solution for enhancing terahertz radiation and developing terahertz lasers.

Acid-Modified Hierarchical Porous Rare-Earth-Containing Y Zeolite as a Highly Active and Stable Catalyst for Olefin Removal.

Rare-earth-containing ultrastable Y zeolite (ReUSY) was modified by oxalic acid solution leaching treatment and applied in industrial units for catalytic olefin removal from aromatic hydrocarbons. The porous structure and amount of acidity of the modified ReUSY (denoted as ReUSY-x, where x indicated the amount of oxalic acid in solution) could be tuned by different concentrations of oxalic acid solution, and the ReUSY-x samples exhibited different catalytic performances. Based on the best catalytic performance of ReUSY-25, an industrial catalyst was prepared and applied in industrial units for catalytic olefin removal. The industrial catalyst exhibited excellent activity and regeneration stability with a long lifetime of about 2 years, which was about 13 times longer than that of activated clay.

Analysis of Clinical and Regional Distribution Characteristics of Obstructive Meibomian Gland Dysfunction in China: A Multicenter Study.

Purpose: To analyze the clinical and regional distribution characteristics of obstructive meibomian gland dysfunction (OMGD) in China. Methods: A total of 2900 patients (2900 eyes) diagnosed with OMGD were enrolled in this multicenter, cross-sectional, observational study. The Ocular Surface Disease Index (OSDI), tear film breakup time (FBUT), Schirmer test (SI), lipid layer thickness (LLT), OMGD grade, meibomian gland loss score (Meiboscore), meibum expressibility score (MES), meibum quality score (MQS), Lid margin abnormality score(LMS) and other tear film stability markers were evaluated. Results: The prevalence of dry eye in OMGD patients was 89%. There were gender differences among OMGD patients in the 30-39 and 50-59 years age groups (p < .05), and FBUT, Meiboscore, MES and MQS were significantly different among different OMGD grades (p < .05). There were significant differences in the detection indexes of OMGD patients in the six regions (p < .05), except LLT (p = .329). According to the Qinling-Huaihe River in China, OMGD patients were divided into the North Group (Shenyang and Beijing) and South Group (Wuhan, Changsha, Chongqing, and Chengdu). There was a significant difference in the detection indexes, except LLT (p = .600), between the two groups (p < .05). FBUT was significantly correlated with the OSDI (r = -0.131; p < .000). Meiboscore and LLT were significantly correlated with the OMGD grade (r = 0.299 and r = 0.106; p < .001). Age, LMS and MQS were significantly correlated with Meiboscore (r = 0.415, r = 0.256 and r = 0.328; p < .001). Conclusions: The prevalence of dry eye was high among OMGD patients. OMGD patients in different age groups may show different gender distributions. The symptoms of patients showed variation among subgroups with different OMGD grades and among different regions.

Widely tunable polarization conversion in low-doped graphene-dielectric metasurfaces based on phase compensation.

We propose a tri-band half-wave plate in the reflection mode, composed of rectangular silicon bar arrays on a 10-layer graphene substrate. By merely varying the Fermi energy of graphene from 0 to 0.25 eV, the three frequency bands shift in step and merge to a continuous dynamic bandwidth from 0.88 to 1.81 terahertz (THz). In addition, it can also dynamically switch the reflected wave among cross-linear polarization, right-handed and left-handed circular polarization in 0.93-1.35 THz. We found that the large dynamic bandwidth originates from the tunable reflection phase from the graphene layers. As it no longer depends on the plasmonic resonance in graphene, the proposed hybrid metasurface offers an alternative solution for active THz polarization devices with low biasing voltages.

Optimized Enhancement Effect of Sulfur in Fe-N-S Codoped Carbon Nanosheets for Efficient Oxygen Reduction Reaction.

The study on the design and preparation of oxygen reduction reaction (ORR) electrocatalysts with high efficiency is currently attracting great concern. Among different types of catalysts, heteroatom-doped carbon-based catalysts have exhibited promising potential, and the exploration of optimized matching of the doping elements is crucial to the design and fabrication of this category of catalysts. Herein, by annealing commercially available and cost-effective precursors, Fe-N-S codoped graphene-like carbon nanosheet catalysts were prepared. The atomically dispersed Fe atoms coordinated with the N atoms to form FeN4 sites as proved by X-ray absorption spectroscopy. By facile modulation of the relative amount of the precursors, the contents of thiophene-S (Th-S) and Fe-N4 sites could be tuned and a series of catalysts with different Th-S/Fe ratios were prepared. The doped sulfur exhibited an enhancement effect on ORR performance, and strikingly, the enhancement efficiency could be optimized by fine modulation of the Th-S/Fe ratio in the catalysts. Furthermore, it was found that when the Th-S/Fe ratio reached an optimal value of 1.8, the ORR performance was significantly boosted, especially in acidic media. The experimental data were supported by density functional theory calculation results, which indicated that the ORR overpotential of the S2(FeN4) configuration model (corresponding to the Th-S/Fe ratio of 2) was lower than that of S3(FeN4) and S1(FeN4). The optimized catalyst (denoted as FeN/SNC-900-3) displayed highly efficient ORR activity in both alkaline and acidic media. In alkaline media, the half-wave potential was 49 mV more positive than that of the commercial Pt/C catalyst, and in acidic media, the half-wave potential was close to that of Pt/C. Moreover, the stability of FeN/SNC-900-3 was outstanding, and the relative current density showed only a slight decay in both alkaline and acidic media after 40,000 s. A primary Zn-air battery with FeN/SNC-900-3 as the cathode catalyst exhibited a high peak power density of up to 153 mW cm-2 and superior cycling stability over 200 cycles.

Polyelectrolyte-Surfactant Mesomorphous Complex Templating: A Versatile Approach for Hierarchically Porous Materials.

Hierarchically porous materials have attracted great attention because of their potential applications in the fields of adsorption, catalysis, and biomedical systems. The art of manipulating different templates that are used for pore construction is the key to fabricating desired hierarchically porous structures. In this feature article, the polyelectrolyte-surfactant mesomorphous complex templating (PSMCT) approach, which was first developed by our group, is elaborated on. During the organic-inorganic self-assembly, the mesomorphous complex of the polyelectrolyte and oppositely charged surfactants would undergo in situ phase separation, which is the key to fabricating hierarchically porous materials. The recent progress in the utilization of the PSMCT method for the synthesis of hierarchically porous materials with tunable morphologies, mesophases, pore structures, and compositions is reviewed. Meanwhile, the functions of the hierarchically porous materials synthesized by the PSMCT method and their applications in adsorption, catalysis, drug delivery, and nanocasting are also briefly summarized.

Deactivation of Cu-Exchanged Automotive-Emission NH3 -SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X-ray Microscopy.

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NOx with an ammonia reductant, we employed scanning transmission X-ray microscopy (STXM) to study Cu-exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000-mile aging. X-ray absorption near-edge structure (XANES) measurements were performed at the Al K- and Cu L-edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi-factor-induced catalytic deactivation. In Cu-exchanged MFI, a transformation of CuII to CuI and Cux Oy was observed. We also found a spatial correlation between extra-framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of CuI and tri-coordinated Al. By inspecting both Al and Cu in fresh and aged Cu-exchanged zeolites, we conclude that the importance of the preservation of isolated CuII sites trumps that of Brønsted acid sites for NH3 -SCR activity.

Bi-functional polarization conversion in hybrid graphene-dielectric metasurfaces.

In this Letter, we propose a hybrid graphene-dielectric metasurface as a bi-functional polarization converter. It can switch between a reflective half-wave plate and a quarter-wave plate around 1 THz by merely applying external biasing voltage, without reoptimizing the dielectric structure. Switching of the two wave plates originates from distinct dispersion of the orthogonal eigenmodes with the chemical potential, which is further explained by the overlapping of graphene and the dielectric resonance modes. Compared with graphene-metallic metasurfaces, a combination of graphene with dielectric microstructures offers an alternative solution for active terahertz devices with high efficiency and large flexibility.